Most passenger vehicles are equipped with a sun visor on both the driver side and the passenger side. The visors are typically located attached to the vehicle headliner along the edge of the vehicle windshield. The sun visors are rotatable between a raised (stowed) position and lowered (deployed) position. In the stowed position, the visor is extends rearwardly along the headliner in a generally horizontal position so that the visor does not block the windshield. In the deployed position, the visor extends downward to block some of the light that has entered through an upper portion of the windshield. Many sun visors can also be rotated away from the windshield to the side door window to block glare when sunlight is entering from the side of the vehicle. By blocking the light entering through the upper portion of the windshield or the side window, visors decrease glare to the driver and passenger, increasing safety and comfort during bright conditions. However, by their nature, sun visors tend to reduce a driver's visibility by reducing the area of the windshield through which objects outside of the vehicle are visible.
Some vehicles utilize tinted windows to reduce glare. Tinted windows generally are formed by applying a coating to a window, wherein the coating filters out light from various parts of the spectrum, such as ultraviolet light.
The effectiveness of window tint is typically classified as visible light transmission (VLT). VLT is the measurable amount of incident light that travels through a medium. More specifically, VLT is typically expressed as percentage of visible solar light, i.e., daylight, that travels through a material. Accordingly, a higher VLT is indicative of a material that allows more sunlight to pass through (a lighter tint), and a lower VLT indicates that the material restricts more light from passing through (a darker tint).
Individual states have laws mandating a minimum VLT for tinted windows on vehicle, i.e., how dark can the tint be. The minimum VLT varies by window and by state, but the minimum VLT for a front windshield is typically in the range of 33% to 50%.
While tinted windows can be effective for reducing glare, they are not without limitations. As noted, there are legal limits to how dark a tint may be. However, perhaps the biggest drawback to tinted windows is the inability to adjust to different lighting conditions. Because the VLT of a tinted window is fixed, the tint may filter out too much light under low light conditions. Conversely, a tinted window may be such that not enough light is filtered out under bright conditions. Thus, there is a need to provide a glare reduction system wherein the amount of glare reduction can be varied to accommodate different conditions.